1. Field of the Invention
The invention is in the field of natural products chemistry. In particular, disclosed is a process for purification of a mixture of carotenoids from palm oil concentrate to produce a crystalline mixture of α-carotene, β-carotene, γ-carotene, and ε,ε-carotene as well as a product enriched in geometrical isomers of β-carotene (9-cis-β-carotene, 13-cis-β-carotene) and α-carotene as well as ε,ε-carotene and γ-carotene.
2. Related Art
The total concentration of carotenoids in crude palm oil is quite low, i.e., approximately 710 ppm. The major carotenoids in palm oil are α-carotene and β-carotene and to a lesser extent γ-carotene. Minor quantities of ε,ε-carotene, a cis-isomer of α-carotene, 9-cis-β-carotene, and 13-cis-β-carotene are also present in palm oil. Since with the exception of ε,ε-carotene, the rest of these carotenoids are precursors of vitamin A, crude palm oil is commercially processed to remove most of the oils and produce a product which is highly concentrated in carotenes. The resulting palm oil carotene concentrate is currently used as a nutritional supplement as well as a food coloring additive. In the course of the past several decades numerous extraction methods have been developed to recover the carotenoids from crude palm oil (GB 1515238 (1976), JP 61109764 (1986), GB 2160874 (1986), EP 0242148 (1987), AU App. No P18770/88 (1988), GB 2218989 (1989), U.S. Pat. No. 5,157,132 (1992)). The classification and assessment of the proposed and patented methods for the industrial production of palm carotenes has been published in a review article by Lenfant and Thyrion OCL-Oleagineux Corps Gras lipides, 3: (4) 294–307, 1996. Because the exposure of carotenoids to oxidizing species present in air, as well as heat, light, and acids results in degradation and losses of these compounds, many of the proposed refining processes for industrial production of a carotene-rich palm oil concentrate are not economically viable. The Lion Corporation of Japan has successfully developed a unique patented process that produces several carotene-rich palm oil concentrate ranging from 2% to 30%. In the initial step of this process, most of the fats and oils are removed by solvolytic micellization (JP 61109764 (1986), BP 2160874 (1986), EP 0242148 (1987)). This results in a palm oil concentrate with 2% carotene content which is then subjected to molecular distillation to remove the volatile oils. As a result, a palm oil carotene concentrate is obtained with a total carotene content of approximately 20%. In the final step of this process developed by Lion, the palm oil carotene concentrate is purified to greater than 95% by chromatography on industrial scale to give a crystalline mixture of carotenoids (EP 0242148 (1987)). The resulting mixture of carotenoids is suspended in vegetable oil to produce the commercial palm oil carotene concentrate with a total carotene content of 30%. To date, the process developed by Lion remains as the only commercial source for the production of a crystalline mixture of palm oil carotenoids with a purity in excess of 95%. The only drawback with this method is that the chromatographic purification of carotenoids by this technique on an industrial scale is quite costly. Another commercially available palm oil concentrate with approximately 20% total carotene content is produced in Malaysia according to a proprietary process; this process does not isolate a crystalline mixture of carotenoids.
As mentioned above, palm oil carotenoids include (6′R)-β,ε-carotene (α-carotene), β-carotene (trans+cis), ε,ε-carotene, and γ-carotene. While numerous synthetic methods have been developed for the laboratory and pilot plant scale preparation of these carotenoids, only β-carotene is currently manufactured on industrial scale. Synthetic methods for commercial production of carotenoids are quite costly because they involve numerous steps in which the precursors to these compounds have to be purified to remove the unchanged starting materials and the undesirable side products. In addition, these synthetic pathways normally use organic reagents, which are toxic and harmful to humans. Therefore, the presence of possible residual contaminants in carotenoids prepared by synthesis is a major deficiency and concern with products of this nature.
Among the carotenoids isolated from palm oil, α-carotene has been shown to serve as an excellent cancer chemopreventive agent in comparison with β-carotene (Murakoshi et al. Cancer Research, 52: 6583–87, 1992). In the above study, the potent preventive action of α-carotene against spontaneous liver carcinogenesis and promoting stage of lung and skin carcinogenesis in mice were suppressed more effectively by α-carotene than by β-carotene. Other than the chromatographic procedure employed by Lion, crystalline palm oil carotenoids which, in addition to β-carotene, include α-carotene and γ-carotene are not commercially available by any other means. In addition, the natural form of α-carotene [(6′R)-β,ε-carotene] is optically active and as a result its commercial preparation by known synthetic procedures is not economical.
This invention was developed because there are no reports on purification of carotenoids from palm oil concentrates that separates the crystalline carotenes from oil by a simple method. The purification and isolation of palm oil carotenoids in crystalline form allows the micronization of these pigments into water dispersible beadlet which is the most preferred formulation for carotenoids as a nutritional supplement (Auweter et al., Angew. Chem. Ind. Ed. 38: 2188–2191, 1999). The process described here provides a convenient and an economical route to purification of a crystalline mixture of carotenoids from commercial palm oil with 2% and 20% total carotene content. This process has also been successfully employed to remove the vegetable oil from the 30% commercial palm oil carotene and recovers a crystalline mixture of carotenoids in excellent purity.